1. Field of the Invention
The present invention relates to tunable solid state lasers, and more specifically, it relates to a tunable diode side-pumped Er:YAG laser.
2. Description of Related Art
In recent years, interest in the development of tunable solid state lasers has increased significantly. A room temperature, tunable solid state laser that operates in the two-micron range is taught in U.S. Pat. No. 4,969,150, which is directed to an end-pumped, ion-doped, solid state laser for producing a CW emission over the approximate spectral range of 1.86 to 2.14 microns.
Neodymium solid-state lasers (e.g., Nd:YAG) are widely used in a variety of applications. One problem with neodymium lasers is that they have moderate efficiency. Neodymium has a narrow absorption band (about 3 nm). Consequently, the pump diodes must be carefully engineered and cooled to keep them at the same wavelength. Precise temperature control is required, consuming a great deal of power for refrigeration. Moreover, neodymium has a short fluorescence lifetime. For a diode-pumped laser, this dramatically increases the cost of the system, since a large number of expensive diode arrays are required for operation.
A variety of methods have been employed for optically pumping solid-state laser. A common method is to use an arc lamp or other similar light source to excite a laser rod. The light source and rod are positioned within and at different foci of a highly reflective housing of elliptical cross-section. This method typically requires relatively large diameter laser rods to efficiently absorb enough of the pumping light emitted by the light source to allow solid-state laser operation. For some industrial operations such as processing electronic materials, compact diode-pumped solid state lasers offer numerous advantages. There are several different methods for diode-pumping solid state lasers.
Diode-pumped Er:YAG lasers have been low power (200 mWatts), end-pumped monolithic devices. Monolithic lasers do not lend themselves well to tunability. In order to tune, monolithic lasers need a change in the index of refraction. This is usually induced by the pump beam. The index changes are small, and consequently, the tuning range of a monolithic laser is limited to .about.1 nm. A key parameter in determining the tuning range of the laser is the gain-to-loss ratio. Due to the large number of surfaces encountered in a discrete-element cavity, discrete-element lasers tend to have higher loss than monolithic lasers. Consequently, greater gain disposition is needed to extend the tuning range.